Frames and racks are commonly used for all types of electrical components to serve as a common support and electrical ground. Generally, such frames tend to be designed for a single application and incapable of variation in dimension or function.
In the past, most electrical and electronic components were quite large, and this factor determined the size and configuration of the mounting frame. As electronic components have decreased significantly in size, there has been some degree of development in connection with mounting frames, but it has not been nearly as significant as in the components themselves.
Because of the decreased size of electronic components, printed circuit boards or cards are now commonly and widely used. These cards house sophisticated and complex electronic circuitry, and typical electronic systems involve the use of several cards that are supported in a single rack or cage and commonly connected into the electronic system.
Because each electronic system and its associated circuitry may be quite unique, frame systems generally are specifically designed to the physical requirements of the systems. Although the electronic and electrical components themselves have become modular in form, as evidenced by the use of printed circuit boards and cards, there has not been any substantial effort to offer a purely modular frame mounting system which can be assembled in various sizes and configurations from off the shelf components to house and support printed circuit cards as well as the heavier and larger attendant components, such as the power supplies, blowers, speed controls and the like.